Intravascular catheters are used in a variety of therapeutic and diagnostic techniques. For example, in angioplasty procedures to treat stenotic arteriosclerotic disease, a catheter having an expandable section, such as a balloon at the distal end, is inserted into and guided through the vascular system. When the balloon is positioned adjacent the stenotic lesion to be treated, the balloon is inflated to compress the stenotic plaque against the blood vessel wall, thereby improving blood flow through the artery. Angioplasty is widely used for reducing stenotic lesions in the coronary arteries, although stenoses in other parts of the vascular system may also be treated.
Other types of intravascular catheters are also known that include a rotatable cutter at the distal tip which, when activated, excises obstructive lesions (see, e.g., U.S. Pat. No. 4,784,636). Catheters incorporating fiberoptic bundles to remove arterial plaques via directed laser light are also known (see, e.g., U.S. Pat. No. 4,669,465).
Catheters which are directly involved in improving blood flow through an artery (whether by expansion, excision or ablation) are typically termed "working catheters." To position a working catheter near the treatment site within the blood vessel, a guide catheter which is distinct from the working catheter may be used. Typical guide catheters comprise an elongated flexible tube having an internal lumen sufficiently large to receive and pass the working catheter therethrough.
Angioplasty, for example, is commonly performed using a working catheter which has an inflatable balloon at its distal end and commonly referred to as a dilatation or balloon catheter. During insertion the balloon is typically deflated and once positioned the balloon is inflated, for example, by filling with fluid under pressure.
Dilatation catheters typically include over-the-wire and on-the-wire type catheters. An over-the-wire catheter contains an inflation lumen by which the balloon is inflated when positioned, and a separate guide wire lumen through which a guide wire is advanced into the vasculature. The dilatation catheter is advanced by alternately advancing the distal end of the guide wire, then advancing the catheter over the guide wire.
In contrast to an over-the-wire catheter, one type of on-the-wire dilatation catheter contains a core wire which is integral with the dilatation balloon. In such a catheter, the core wire, balloon and inflation lumen form a single unit. Typically a flexible distal tip made of helically coiled wire is provided at the distal end of the core wire. The flexible distal tip may be bent at a predetermined angle to facilitate steering of the core wire to a desired blood vessel at a branch point by selectively rotating a proximal end of the core wire while viewing the distal tip by fluoroscopy.
U.S. Pat. No. 5,312,340 to Keith entitled Balloon Dilatation Catheter Having Dual Sealing Plugs discloses a catheter in which a sealing plug extending annularly about the core wire separates the distal end of the balloon member from the flexible coil tip. The flexible coil tip is attached to the core wire by solder or braze. In one disclosed embodiment, the distal end of the balloon extends over the proximal portion of the flexible coil tip, which is soldered or brazed to the core wire. The balloon material is not joined or sealed to the flexible coil tip, allowing the balloon to rotate about the flexible coil tip and the core wire.
In a typical on-the-wire balloon catheter, the distal end or leg of the balloon is connected to the core wire, and the flexible tip is secured to a portion of the core wire which extends distally beyond the balloon. For example, U.S. Pat. No. 4,771,778 to Mar entitled Steerable Low Profile Balloon Dilatation Catheter discloses a balloon catheter having the distal end of the balloon secured to the core wire using means such as an adhesive, and a flexible coil spring tip secured to the core wire by means such as solder. Similarly, U.S. Pat. No. 5,156,595 to Adams entitled Dilatation Balloon Catheter and Method of Manufacture discloses an on-the-wire balloon catheter having a core wire with a flexible coil spring extending distally therefrom. The distal balloon end is attached to the core wire using an adhesive such as epoxy; and the flexible coil spring is secured to the core wire using a braze or solder connection.
U.S. Pat. No. Re. 33,166 to Samson entitled Steerable Dilatation Catheter discloses a dilatation catheter wherein the balloon is secured to the core wire by adhesive, and the flexible helical coil is connected to the core wire by epoxy. A filler, such as epoxy, is used to define a smooth transition region between the distal end of the balloon and the proximal end of the flexible helical coil. The patent further discloses that means other than adhesives can be used to secure the balloon to the core wire, such as direct fusion or the use of a clamp.
In other types of on-the-wire catheters, solder is commonly used to connect the proximal end of the coil spring to the core wire. The distal portion or leg of the balloon is positioned over the soldered area and reheated to cause the thermoplastic balloon material to melt and fuse onto the coil spring and core wire. Unfortunately, solder may reflow distally along the core wire when the balloon is heated. The reflowed solder wicks forward along adjacent coils of the coil spring toward the distal end thereof. The reflowed solder, once cooled, results in an area of increased stiffness along the distal tip adjacent the distal end of the balloon. Accordingly, the distal tip is no longer flexible along its entire length as is desirable to facilitate bending and steering of the core wire through the vascular system.